The present invention relates generally to molding apparatus and more particularly to a molding machine wherein foundry molds may be simultaneously compressed and vibrated between a vibration table and a presser plate.
In prior art devices, it has been known to produce foundry molds by effecting a desired distribution of the granular molding material in a process which involves compression and jarring or vibration of the mold assembly. In some cases, a vibration operation is followed by a subsequent compression step while in other cases simultaneous vibration and compression may be performed after an initial compression operation.
Experience indicates that an economical way of producing a mold consists of compressing the granular material of the mold by squeezing together the mold parts. However, the disadvantage of this type of production process is that the compressive forces produced above the mold patterns is usually too great while the forces created in the dividing plane of the mold is low. Particularly, it has been found that the compressive forces effected between the patterns and the edges of the mold in the dividing plane are unsatisfactory.
If the mold granular material is only compressed by jarring during the production of the foundry mold, the compression which is effected is insufficient. It has therefore been common to produce a mold by effecting an initial compression thereof in a first operation utilizing a jarring technique and by completing the compression in a subsequent operation which involves squeezing or impact molding. Impact molding usually involves the application of impact forces by a jarring piston to either the squeezer board, the molding table or both during and simultaneously with the squeezing process. However, it has been found that the granular material which is to be compressed does not change its state of motion or its state of rest. In this connection reference is made to U.S. Pat. No. 1,814,416.
This type of foundry mold production technique exhibits considerable differences in the compression of the granular material. Again, it is found that the degree of compression is overly high above the molding patterns while compression in the dividing plane of the mold, particularly between the patterns, drops sharply. As a result, the degree of utilization of the mold surface is reduced because, in order to improve the compressive effects between the patterns, the distance between the patterns must be selected to be greater than is desired.
Uniform compaction of the granular material may be achieved in a process which involves preliminary compression of the granular material in a first operation with completion of the compression being performed in a second operation involving simultaneous jarring and squeezing. This type of production technique not only yields the most uniform compaction of the granular material, particularly at the edges of the dividing plane, but it also permits selection of smaller pattern intervals on the pattern plate thereby enabling substantial improvement in the utilization of the mold surface.
Attempts have been made at an early stage to effect compaction of the granular material by simultaneous vibration and compression by utilizing an adjacent press to exert upon the granular material a squeezing pressure during the jarring operation. In this connection reference is made to British Pat. No. 571,188 and particularly to lines 40-43 on page 2 thereof. The lifting force of the jarring piston must be selected great enough that it may lift, in addition to the weight of the mold table and of the parts connected thereto, the squeezing pressure acting additionally upon the granular material. However, the above mentioned device for simultaneous jarring and squeezing, which in itself may be quite simple, is not applicable in a practical sense because the falling movement during the jarring process exceeds the acceleration due to gravity. This produces the result that all the parts are not rigidly connected with the jarring table just at the time that the molding box, the sand frame and the like are lifted from the molding table during the jarring operation.
Additionally, vibratory molding apparatus is known which involves a squeezer board operating under a liquid or air pressure wherein the squeezing device is carried by a jarring table for the purpose of vibration-compression. A squeezing or compression device is arranged on a swivel squeezing plate which bears over a column upon the jarring table. The swivel squeezing board may be swung into an operating position over the jarring table after the molding box has been attached and the box has been filled with the granular material. On the opposite side of the squeezing board there is arranged a tie-rod which is articulated to the jarring table when the squeezing board is swung into place so that a portal is formed above the jarring table to absorb the squeezing pressure. (See German Pat. No. 531024.) This type of molding machine intended for the simultaneous vibration and compression of a mold has been found unacceptable from the practical point of view because the necessary forces for swinging the vibration-compression machinery in and out of position, and thus the time required for this operation, render practical application thereof unlikely.
Molding equipment is also known wherein a press is arranged upon a pivotable arm which is mounted upon a column and which is connected over a support and a bolt with both a jarring cylinder and with a jarring table. (See British Pat. No. 350020, particularly lines 18-25 on page 5 thereof.) This type of molding equipment not only involves disadvantages similar to those of the device disclosed in German Pat. No. 531024, but it also includes the additional disadvantage that the compression pressures which already amount to several tons for small molds if they are to be effective, can no longer be applied in the form of a yoke with a great sweep.
Furthermore, a molding machine for effecting jarring and squeezing, or both, is known wherein a press is articulated to a mold table or the parts are connected to the mold table only during compression or vibration-compression but otherwise has no physical contact therewith. (See Swiss Pat. No. 315945.) This molding machine has the disadvantage that the press must, in one case, be swung out for attaching the molding box, filling and precompressing of the granular material by jarring, and subsequently it must be swung in again over the mold table for final compression by jarring or by jarring and squeezing. Thus, in this case there also arise the aforementioned disadvantages related to the devices described in German Pat. No. 531024 and in British Pat. No. 350020. This molding machine, however, can also be built for use in an application which involves operation of the device in a carousel fashion wherein a turntable carries several jarring units with the respective jarring tables, pattern devices and molding boxes. In this case, several operations are performed in the successive stages which involve (1) attachment of the molding box on the complete pattern device, (2) filling-in and precompression of the granular material by jarring, (3) final compression by jarring or by jarring and squeezing, and (4) lifting of the mold from the pattern device in a final stage of operation. This last application has the disadvantage that extremely large masses must be moved since several jarring units with the pattern devices, the molds or molding boxes, must be arranged on the turntable. This type of molding machine therefore involves the disadvantage that it requires a rather complicated drive since large forces must be transmitted, so that an inordinately high cost is involved in the maintenance and operation of the device. Experience has shown that the mold sizes for molding on molding machines becomes increasingly larger. Consequently, the dimensions and weights which these molding machines require become so great that they can only be produced in relatively few machine plants.
Thus, it will be seen, that with prior art devices, disadvantages and difficulties will arise in connection with the practical application of known techniques where compression and vibration of a mold, either separately or simultaneously, is to be effected. The present invention is intended to eliminate many of the difficulties and disadvantages of the prior art and to provide equipment which is practical in its application and effective in its use. By the present invention, handling of foundry molds during compression and/or vibration thereof is simplified and the size and weight of the structural parts which are required are reduced. Additionally, lower driving forces may be utilized and the costs of operation and maintenance of equipment is also reduced.